Simulation and design of (In, Ga)N-based light emitting diode

Indium gallium nitride, (In,Ga)N, is a promising semiconductor to power the next generation of light emitting diode technology. Its main advantage resides on the possibility of directly converting electrical energy into light without the use of down-converting phosphors. Current challenges to realize the potential of such technology include a high density of threading dislocations, large lattice mismatch between the InN and GaN phases, and built-in electric field induced by spontaneous and piezoelectric polarizations. In this context, template-assisted heteroepitaxially growth of GaN nanorods with pyramidal caps offer a low-cost solution to remove these limitations and improve device efficiency. In order to understand and then engineer the topology of these three-dimensional devices, a continuum theoretical framework was numerically implemented to account for: 1) the image forces exerted on dislocations, 2) internal stresses in the nano-heterostructures and 3) the self-induced electric fields in the quantum well region. Simulations demonstrate that the nanorod heterostructure displays stress-free regions at the apex and side edges of the pyramidal cap, which favors piezoelectric polarization relaxation. Furthermore, nanorod geometries with radius of ∼26 nm and height of ∼65 nm offer a dislocation filtering probability of 95%. Such designs have been verified experimentally. In addition, the nanorod geometry displays semipolar orientations that deliver an order of magnitude reduction in built-in electric field (in the range between 0.34 MV/cm and 2.67 MV/cm) compared to the thin-film configuration (5.7 MV/cm). It is also demonstrated that the ratio of quantum well thickness versus cladding layer thickness controls the built-in polarization. A zero built-in electric field is predicted for a thickness ratio of 1.28, in the limit of thick cladding layers.